Recently, display technologies using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD) and the like that are used instead of a known brown tube in accordance with the development of optical technologies are suggested and sold. The higher properties of the polymer material for displays are required. For example, in the case of the liquid crystal display, according to the development toward the thin film, the lightness, and enlargement of the screen area, the wide viewing angle, the high contrast, the suppression of change in image color tone according to the viewing angle and the uniformity of the screen display are particularly considered as important problems.
Therefore, various polymer films such as a polarizing film, a retardation film, a plastic substrate, a light guide plate and the like are used.
Currently, various modes of liquid crystal displays such as twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS) liquid crystal cells are developed. Since all of these liquid crystal cells have intrinsic liquid crystal alignment, they have intrinsic optical anisotropic property, and in order to compensate the optical anisotropic property, a film in which a retardation function is provided by stretching various kinds of polymers has been suggested.
This retardation film is produced through a method such as vertical monoaxial stretching, step biaxial stretching, simultaneous biaxial stretching and the like after various polymer films are produced. The retardation film that is produced through the stretching process has the positive in-plane retardation value and the negative thickness retardation value, and these films can be applied to a VA (Vertical Alignment) mode of the liquid crystal modes.
In particular, in the IPS (in-plane switching) mode of the liquid crystal modes, the retardation film that has the positive in-plane retardation value and the positive thickness retardation value is required, the molecules of the most polymer films are arranged in a stretching direction while stretching is carried out, and it has the positive in-plane retardation value and the negative thickness retardation value.
In general, a compensation film for IPS mode compensates a viewing angle by uniaxially stretching a COP (cyclic olefin polymer) and coating a nematic liquid crystal that is the +C plate. However, in this case, since the birefringence of the liquid crystal is very high, when the alignment and the coating thickness of the liquid crystal are slightly changed, the retardation of the entire compensation film is largely changed. Thus, in the case of thin film, there is a problem in that it is difficult to control the retardation. In addition, because of the cost of the expensive liquid crystal, the production cost is increased. Therefore, there is a disadvantage in that it is difficult to generally commercialize it.